THE ELECTRIC TELEGRAPH. 



When the arm of c' is vertical, no current can pass from B' to L r 

 and consequently the needle of o will remain in the vertical 

 direction, without deflection. If the upper arm of c' be turned to 

 the right, r, the current from B', passing along L, will flow through 

 the coil of the galvanometer at s, and will deflect the indicating 

 needle to the right, so that it will lean upon the right hand stud, R. 

 If c' be then turned back to the vertical direction, the current 

 will be suspended, and the needle at s will return to the point o. 

 If the upper arm of c' be then turned to the left, 7, the current 

 will be again transmitted upon the line-wire, L, but in a direction 

 contrary to its former course, and thus passing through the gal- 

 vanometer at s, in a contrary direction, the needle, which was 

 before deflected to the right hand stud, E, will now be deflected to 

 the left hand stud, L. 



Thus, it appears, that according as the upper arm of c' is turned 

 to the right or left, or placed in the vertical position, the needle 

 on the dial at s, is also turned to the right or left, or placed in 

 the vertical position. 



In a word, whatever position is given to the handle of the com- 

 mutator at s', a corresponding position is assumed by the indicat- 

 ing needle at s, and these changes of position of the indicating 

 needle at s, are absolutely simultaneous with the changes of 

 position of the handle of the commutator at s'. 



The manner of expressing the letters and figures, is by making 

 repeated deflections of the needle right and left, making a short 

 pause at the end of each letter signal. Thus two deflections to 

 the left express A ; three, B ; four, c ; while one expresses the 

 completion of a word. One to the right expresses M ; two, BT ; 

 three, o ; and four, p. In the same manner, L is expressed by 

 four deflections, which are, successively, right, left, right, and left. 



As these signs are purely arbitrary, and may be changed in 

 every independent telegraph, it is not necessary here to notice 

 them further. 



Besides the signals which express letters and figures, it is usual 

 to adopt others to express words or phrases of very frequent 

 occurrence, such as, I don't understand, I understand, wait, go- 

 on, repeat, &c. 



It is usual, though not necessary, for the agent who sends a 

 dispatch, to pass the current through his own instrument, so that 

 his indicating needle shows exactly the same deflections as the 

 indicating needle of the station he addresses. Thus, when s' 

 addresses s, his own indicating needle, o', speaks as well as the- 

 indicator, o, of the station, s. 



All that has been stated in (111) et seq. of the transmission of 

 the same despatch through a series of stations, of cutting off the 

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